Spoffle's claim for themself is credible. Spoffle's claim for lots of other people is not credible by itself. Treating unsubstantiated claims for millions of poeple as credible just because someone makes the claim is not a matter of civility.
And yes, some sweeteners have a bitter aftertaste for some people. As you note, that's why sweeteners are often combined in order to counter that effect. Can you provide some evidence to support your claim that it doesn't work for a lot of people? Also, how many are you counting as "a lot" in this context? 10,000 people is a lot...but not as a percentage of billions.
There have been studies showing both ways, even if you exclude the studies on mice. I'm not advocating for all sugar to be replaced with sweeteners, certainly not the ones available today. Some of the claims about them are bunk, but there's enough evidence of adverse effects or ineffectiveness to make some caution a good idea. Which is why I now drink mostly water.
There are still plenty of fizzy drinks that don't contain sweeteners other than sugar. If they now contain lots of sugar but not as much as before (e.g. 7-up reduced sugar from 38g in a 330ml can to 26g in a 330ml can), you're free to add more sugar to them yourself if you like.